Hi, l just wanted to know if the fibre gear on a BTH magneto on a twin should have much backlash when cold, as mine has hardly any. ( I note that the Vincent instruction sheets say to have no less than 8 thou backlash for the original ATD) My problem is the breather pinion with which it meshes overheated and welded itself on to it's spindle with the alloy from the steady plate. Consequently the whole lot was turning in the case with the tab washer tearing a big hole in the steady plate . I'm trying to find if the cause is the expansion of the fibre gear.